Influence Of Contact Geometry Research Articles

Numerical investigations on the lubrication characteristics of involute harmonic gears

PurposeHarmonic gears always work under different operating conditions and may usually break down due to lubrication failures, while its lubrication mechanism is still not clearly understood. This paper aims to present a lubrication model comprehensively considering the influence of contact geometry, lubrication properties and three-dimensional (3D) real surface roughness to analyze the lubrication performance under different conditions.Design/methodology/approachBased on the discrete convolution-fast Fourier transformation with duplicated padding and quasi-system numerical methods, the lubrication model for harmonic gears is developed, which is verified by comparing results with available lubrication data.FindingsThe effects of meshing process, working conditions and 3D roughness on the lubrication characteristics are discussed. From the calculated cases, the increase in rotational speed and decrease of applied torque may increase the film thickness, enhancing the lubrication performance of harmonic gears. It is also observed that proper surface roughness can be used for lubrication design.Originality/valueThe research results can provide theoretical guidance for improving lubrication performance and reducing friction/wear of the harmonic gear interfaces. This study can be promoted to various engineering scenarios of harmonic gears, such as industrial robots, space-driven agencies and precision measuring instruments.

Tribocorrosive Aspects of Tungsten Carbide, Silicon Nitride, and Martensitic Steel under Fretting-like Conditions

Water-based lubrication faces the common challenge of component lifetime extension which is impaired by tribocorrosion due to material surface depassivation. However, such mechanisms in a pH-neutral and low-halide electrolyte require additional understanding. A ball-on-flat configuration study of hard-phase materials in a low amplitude–high frequency sliding contact against martensitic chromium steel with contact pressures around 200 MPa is presented. Under lubrication by purified water, tungsten carbide-based metal matrix composite (MMC) with NiCr binder and silicon nitride-based ceramic (SiAlON) against DIN/EN 1.4108 steel yielded coefficients of friction above unity. Wear scar enlargement led to fretting-like conditions with adhesion becoming the fundamental wear mechanism. A tribocorrosion-induced depletion of tungsten carbide and nickel was determined for MMC. SiAlON materials suffered extreme wear under the formation of abrasive SiO2, while heat-treated DIN/EN 1.4125 steel showed lower friction and wear, but also showed signs of hydrogen embrittlement. Results from accompanying single-material corrosion experiments could not satisfactorily explain the phenomena. Including galvanic interaction and the influence of contact geometry, a new tribocorrosion model for fretting conditions is proposed. It describes an expanding anodic belt located at the inner-most crevice position of an otherwise cathodically polarized material. Low conductivity of the electrolyte is seen as a key player in this process, while the galvanic situation between two materials in contact was shown to invert when water was substituted by a wet organic phase.

Influence of contact geometry over the filament bond of polylactic acid blends

Fused Filament Fabrication is one of the most common Additive Manufacturing technologies among industrial and domestic users because of the satisfying quality of parts and the great variety of thermoplastic polymers available on the market. New possibilities were provided along with the equipment with multiple extrusion systems, referring to multi-colour and multi-material components. Besides part orientation during the manufacturing process, filament bond influences the mechanical properties of parts produced through Fused Filament Fabrication technology. This paper aims to investigate if the bond performance for polylactic acid-based polymers can be enhanced by designing new contact geometries, different from the current surface-to-surface approach. To comprehensively understand the influence of the designed bonding geometries over the tensile strength, all specimens were produced according to a factorial design of experiment method and contact geometries constrained with function related to the nozzle size.

Strength of adhesive contacts: Influence of contact geometry and material gradients

The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces. In the past, the influence of roughness has been investigated thoroughly. However, even in the presence of perfectly smooth surfaces, geometry can come into play in form of the macroscopic shape of the contacting region. Here we present numerical and experimental results for contacts of rigid punches with flat but oddly shaped face contacting a soft, adhesive counterpart. When it is carefully pulled off, we find that in contrast to circular shapes, detachment occurs not instantaneously but detachment fronts start at pointed corners and travel inwards, until the final configuration is reached which for macroscopically isotropic shapes is almost circular. For elongated indenters, the final shape resembles the original one with rounded corners. We describe the influence of the shape of the stamp both experimentally and numerically.Numerical simulations are performed using a new formulation of the boundary element method for simulation of adhesive contacts suggested by Pohrt and Popov. It is based on a local, mesh dependent detachment criterion which is derived from the Griffith principle of balance of released elastic energy and the work of adhesion. The validation of the suggested method is made both by comparison with known analytical solutions and with experiments. The method is applied for simulating the detachment of flat-ended indenters with square, triangle or rectangular shape of cross-section as well as shapes with various kinds of faults and to “brushes”. The method is extended for describing power-law gradient media.

The effect of contact geometry on fretting wear rates and mechanisms for a high strengthsteel

This paper investigates the effect that contact geometry on fretting wear rates and mechanisms for non-conforming contacts. Tests have been conducted in the gross sliding regime under a constant normal load in a cylinder-on-flat configuration with a high strength steel for a range of cylinder radii. Two distinct damage mechanisms have been identified, with the operative mechanism depending upon contact geometry. Fretting of less conforming contacts results in higher wear rates compared to that associated with more conforming contacts where the wear rate is significantly lower (between 20% and 50% of that of the less conforming contacts) in addition, much higher levels of adhesive transfer are observed in more conforming contacts, with beds of metallic debris particles being evident. It is proposed that the dependence of wear rate and mechanism on the contact geometry is not associated with differences in contact pressure (although these do exist), but is associated with the influence of contact geometry on debris flow out of the fretting contact and on the effectiveness of oxygen being excluded from the centre of the fretting contactpatch.

Influence of Contact Geometry on Local Friction Energy and Stiffness of Revolute Joints

Revolute joints (also called pin joints or hinge joints) are used in many different mechanical systems such as robotic arms, door hinges, folding mechanisms, or hydraulic shovels. Since they transmit forces and give a rotational degree of freedom to the connected parts, revolute joints have a major impact on the dynamic behavior of the system into which they are built. Two main characteristics of these elements are their stiffness and their clearance. Both of them change as the wear between the joint’s pin and the rod hole increases during operation. In order to consider these aspects in a multibody simulation an analytical, numerically effective method has been developed to calculate the stiffness of a revolute joint in dependence of the geometry and the wear state. In addition, the calculation algorithm allows for for the analysis of the local friction energy that occurs in the contact zone. In this paper, the calculation approach is presented together with the results for two different steady loaded revolute joints.

Study of the Influence of Contact Geometry and Contact Pressure on Sliding Distance to Galling in the Slider-on-Flat-Surface Wear Tester

One of the major causes of tool failure in sheet metal forming is wear in the form of galling. Galling is gradual buildup of adhered sheet material on the tool and leads to unacceptable scratches on the sheet surface and to components that fail to meet tolerances. Because it is difficult to reproduce operational and interactional conditions in laboratory test equipments it is hard to test, model, and predict galling initiation. Here the authors examine how changes from elliptical to line contact geometry influenced galling initiation under dry sliding by using a slider-on-flat surface (SOFS) wear tester. A micro clean tool steel was tested against ferritic low-strength and martensitic high-strength steel sheets. The sliding distance to galling initiation was extracted from friction data and verified by scanning electron microscopy (SEM) observations. The presence of adhesive wear on worn tools after completed tests was used as a criterion. Experimental results showed that the elliptical contact causes galling quicker than the line contact. Applicability of experimental results depends on the relevance of test conditions, so contact pressures calculated for the described tests were compared to calculated contact pressures in a semi-industrial U-bending test and to literature data relevant to industrial applications. Good agreement between values observed for SOFS and for most selected industrial applications was found, which assume that contact pressures typical for most common industrial applications can be successfully simulated by selection of tool geometry and normal load in the SOFS tester.

Influence of contact geometry on the magnetoresistance of elliptical rings

Room temperature magnetotransport measurements have been carried out on NiFe single layer and NiFe∕Cu∕Co∕Au multilayer elliptical rings. The shape of the magnetoresistance response is strongly dependent on the contact configuration and the direction of the applied field with respect to the easy axis of the ellipse. The magnetization states and magnetoresistance can be quantitatively modeled.

Influence of contact geometry and molecular derivatization on the interfacial interactions between gold and conjugated wires

Self-assembled monolayers made of thiolated conjugated wires attached on gold surfaces currently attract a considerable interest in the field of nanoelectronics. The interactions taking place at the metal/molecule interface govern the electronic structure of the complex, and hence the barriers for charge injection from the electrodes to the molecules. Considering benzenethiol as a prototype molecule, we investigate here the way the electronic structure is affected by the nature of the anchoring site of the sulfur atom on the gold surface and by the relative orientation of the molecule with respect to the surface. We also assess whether the changes in the molecular electronic properties upon substitution are similar for the isolated molecule and for the molecule attached on the gold surface. Our results provide strong evidences that, in order to introduce functionalities and/or improve charge injection in molecular devices, the electronic properties of conjugated molecular wires can be tailored by derivatization independently of the metal electrodes.

Influence of contact geometry and current on effective erosion of Cu-Cr, Ag-WC, and Ag-Cr vacuum contact materials

Effective ac erosion rates were measured for Cu-Cr, Ag-WC, and Ag-Cr butt-type contacts in vacuum contactors, using half-cycle current pulses of 450-600 A rms. The polarity was changed for each operation to ensure uniform effects for both contacts. The contacts parted during the rising current, with the full gap set to 10-30% of the contact diameter. The effective linear volume erosion rate [cm/sup 3//C] was determined by measuring the axial erosion of the contacts versus the number of operations. This was converted to an effective mass erosion rate [/spl mu/g/C], which was significantly smaller than the reported absolute cathode erosion rate based on measured loss of cathode mass with long square current pulses at large fixed gap. The effective erosion rate increased when spiral-slotted contacts were used. The dependence of the effective erosion rate on the gap was studied, and also the distribution of metal droplets on the arc shield. Most of the droplet flux from the gap was close to the plane of the cathode, while a large fraction of the ionized vapor from the cathode spots was deposited onto the anode. The droplets were a significant fraction of the cathode material loss and the overall effective erosion.

SnO 2 sensors: current status and future prospects

A survey is given on the current status and future prospects in research and development of SnO 2-based sensors. Atomistic models of molecular recognition are discussed first. They include physisorption, chemisorption, surface reaction, catalytic reaction, grain boundary reaction, bulk reaction and three-phase boundary reaction steps. The influence of contact geometry and crystallinity on the sensor response signal is outlined. A brief summary is given of the current status of sensor research and development with emphasis on ceramic, thick-film and thin-film sensors based on crystalline, polycrystalline and nanocrystalline SnO 2. Three different aspects are mentioned in the outline which are expected to lead to significantly improved performances of future sensors: the improved selectivity through the modulation frequency in a.c. measurements, the improved stability through the better control of structures, and the improved selectivity and drift compensation through pattern recognition.